The invention relates to an internal combustion engine comprising an engine braking arrangement in the form of a compression brake.
Patent Specification EP 0 477 579 B1 discloses such an internal combustion engine comprising an engine braking arrangement in the form of a compression brake. The internal combustion engine has an exhaust gas turbocharger, the exhaust gas turbine of which is disposed in an exhaust tract, and the compressor of which is disposed in an intake tract of the internal combustion engine. A power turbine which is driven by the exhaust gas of the internal combustion engine and is coupled to the internal combustion engine via a transmission is provided downstream of the exhaust gas turbine. A bypass device including a bypass pipe which extends around the power turbine and can be opened or closed is provided in the exhaust pipe downstream of the power turbine. The bypass device is designed as a variable switching valve in the form of a butterfly valve. The exhaust gas of the internal combustion engine drives the exhaust gas turbine which drives the compressor via a common shaft. The compressor compresses combustion air and conveys the compressed air into the intake tract of the internal combustion engine. The exhaust gas of the internal combustion engine first flows into the exhaust gas turbine of the exhaust gas turbocharger and then on into the power turbine which supplies the rest of the energy extracted from the exhaust gas to the internal combustion engine via the transmission. In the engine braking mode, the fuel injection is deactivated and the compression brake is activated. At the end of a compression stroke, the compression brake opens for a short period at least one outlet valve provided in the cylinder head. When the outlet valve is open, the compressed air in the combustion space then escapes into the exhaust tract.
During motor braking the internal combustion engine only carries out compression work and thereby generates braking power. The compression work is dependent on the degree of filling of the cylinders. In order to achieve a high degree of filling, the exhaust gas back pressure downstream of the exhaust gas turbine has to be low. However, the power turbine downstream of the exhaust gas turbine constitutes a throttle which increases the exhaust gas back pressure. In addition, the power turbine which is driven by the exhaust gas drives the internal combustion engine. In order to lower the exhaust gas back pressure and avoid the driving of the power turbine, the bypass device opens. The exhaust gas then flows into the bypass pipe past the power turbine. The braking power generated by a pulsed compression brake shows a flat, approximately linear profile over the rotational speed. This means that, at low to medium rotational speeds of the engine, the braking power is relatively low.
It is the object of the present invention to provide an internal combustion engine providing a braking power which is significantly increased at low and medium rotational speeds of the internal combustion engine, that is, an engine whose braking power profile is advantageously high even at medium to high rotational speeds of the internal combustion engine.